This application is based on application No. 97-51254 filed in the Korea Industrial Property Office on Oct. 6, 1997, the content of which is incorporated hereinto by reference.
(a) Field of the Invention
The present invention relates to a method of preparing a microbial culture for wastewater treatment, more particularly, to a method of preparing a microbial culture comprising step of cultivating a microorganism existing in an aeration tank of a wastewater treatment plant.
(b) Description of the Related Art
In a biological wastewater treatment method, many organic materials in wastewater can be decomposed, detoxified and removed by a microorganism. The biological method is classified into an aerobic treatment and anaerobic treatment. The aerobic treatment is classified into an activated sludge process, trickling filter process, rotating biological contactor process, oxidization pond process. The anaerobic treatment is classified into an anaerobic digestion process and septic tank process.
In the activated sludge process, many organic materials in wastewater can be decomposed by an aerobic metabolism of a microorganism.
FIG. 2 shows the conventional activated sludge process. An influent is fed into a primary settling tank (11). A volume and pH of the influent (raw sewage) is controlled in the primary settling tank (11). A solid substance and suspended solid (SS) substance are removed from the raw sewage in the primary settling tank (11). And then, the sewage is fed into an aeration tank (13) continuously. In the aeration tank (13), many organic materials are oxidized and decomposed by aerating with an aerobic microorganism. And then, a mixture of the aeration tank (13) is fed into a secondary settling tank (15) continuously. Sludge floc in the mixture are settled and separated in the secondary settling tank (15). A part of the settled sludge is resupplied to the aeration tank (13) through a return sludge line (19) and the other part of settled sludge is dehydrated and disposed as a waste sludge. A supernatant of the secondary settling tank (15) is sanitized and discharged. The aeration tank playing an important role in the activated sludge process is a concrete construct and contains an activated sludge generally.
A microbial culture for wastewater treatment is a microorganism goods to promote a decomposition of various materials and to decrease BOD, COD and SS concentration, being added to the aeration tank.
The microbial culture for wastewater treatment is classified into a solid type formulation and a liquid type formulation. The solid type microbial culture for wastewater treatment may be prepared by enrichment cultivating a microorganism, inoculating the microorganism to a cereal medium, cultivating, hot-drying and crushing. Otherwise, the solid type microbial culture may be prepared by cultivating an inoculum in a liquid medium, freeze drying the cultured material and mixing the freeze dried material with a rice straw, rice bran, sawdust, fallen leaves or cereal. In a different way, the solid type microbial culture may be prepared by cultivating an inoculum in a liquid medium, adding a surfactant to the liquid medium and spray drying the cultured material.
The liquid type microbial culture for wastewater treatment may be prepared by enrichment cultivating a microorganism in a liquid medium, adding a silicon oil and nonionic surfactant to the liquid medium.
The solid type microbial culture has a relatively long preservation time. However, it has a relatively long activation time. The liquid type microbial culture has a relatively short activation time. However, it has a relatively short preservation time.
To solve the problem of the solid type microbial culture, Korean Patent Laid-Open Publication No. 95-26824 discloses a method of preparing a microbial culture for wastewater treatment using a microorganism separated from soil and adding a sludge as a promoter for the microbial culture.
Korean Patent Laid-Open Publication No. 96-14334 discloses a method of preparing a microbial culture for wastewater treatment adding a skim milk and glutamate to a medium and freeze drying.
To solve the problem of the liquid type microbial culture, Korean Patent Laid-Open Publication No. 96-22289 and No. 96-22288 disclose a method of preparing a microbial culture for wastewater treatment adding a nonionic surfactant and glycerol to a liquid medium and spray drying.
Korean Patent Laid-Open Publication No. 94-6931 discloses a microbial culture for wastewater treatment comprising propionate as a microbial growth inhibitor. The microbial culture has a relatively long preservation time. However, the microbial culture has a relatively low activation.
PCT application publication No. WO 96/15992 discloses a method of treating wastewater comprising steps of adding an aerobic microorganism and an anaerobic microorganism to a fermenter. This method does not generate any offensive odor, toxic gas and harmful substance. An object of the invention is to remove a harmful gas from sewage by using microorganisms separated from nature, not to cultivate microorganisms in the fermenter. This invention has a problem that microorganisms require a relatively long time to adapt to a sludge.
U.S. Pat. No. 5,376,275 discloses a method of treating wastewater comprising steps of fermenting a sewage sludge component for a period of at least 15 days under conditions to maximize the formation of soluble carbonaceous substrates in the sludge component, contacting the fermented sludge component with influent sewage to form a conditioned sewage, the conditioned sewage containing soluble carbonaceous substrates elutriated from the fermented sludge component, and supplying the conditioned sewage to the activated sludge treatment plant. The invention has a relatively long treating time of 15-60 days.
It is an object of the present invention to provide a method of preparing a microbial culture for wastewater treatment having a relatively long preservation time.
It is another object to provide a method of preparing a microbial culture for wastewater treatment having a lot of effective microorganisms to decompose an organic material in the wastewater.
In order to achieve these objects, the present invention provides a method of preparing a microbial culture for wastewater treatment comprising the steps of supplying an aerated material derived from an aeration tank to a bioreactor and cultivating a microorganism existing in the aerated material by adding a culture medium to the bioreactor.
The present invention provides a wastewater treatment plant comprising: a primary settling tank for removing a solid substance and a suspended solid substance from a raw sewage; an aeration tank for decomposing an organic material in a raw sewage by aerating the raw sewage with a microorganism, the aeration tank being linked to the primary settling tank; a bioreactor linked to the aeration tank, the bioreactor being supplied with an aerated material from the aeration tank and a culture medium, preparing a microbial culture by mixing the aerated material with the culture medium, and supplying the microbial culture to the aeration tank; and a secondary settling tank for settling a sludge floc supplied from the aeration tank, the settling tank being linked to the aeration tank.